New Stormwater Tunnel Will Have Storage Capacity of Nearly 60 Million Gallons
October 16, 2020
The final stage of the massive stormwater runoff and sewage collection and treatment project was set in motion, at least in concept, by the Coastal Resources Management Council (CRMC) at its Oct. 13 online meeting. Several issues need to be resolved, however, such as where to dispose of 800,000 tons of pulverized rock and sediment known as tunnel muck.
The Narragansett Bay Commission (NBC), Rhode Island’s largest wastewater treatment operation, manages the massive combined sewer overflow (CSO) system, which is credited with significant pollution reduction in upper Narragansett Bay.
CSO Phase III will divert, store, and treat up to 58.5 million gallons of stormwater and sewage from Central Falls and Pawtucket before it’s discharged into the Blackstone and Seekonk rivers.
A 2.2-mile, 30-foot-wide collection tunnel will run from Pawtucket to the NBC’s Bucklin Point wastewater treatment facility in East Providence. The tunnel will be dug at a depth of 150-200 feet along the rivers’ eastern shoreline.
The final plans have yet to be completed and submitted to CRMC, but the project will have a tunnel pump station, four drop shafts, and a tunnel odor-control facility. Two additional treatment clarifiers — to remove suspended solids — will be built at Bucklin Point.
Future exceptions and variances would require CRMC approval. NBC is reviewing tunnel muck disposal locations with the Rhode Island Department of Environmental Management.
Structures on nine properties, including homes, in East Providence and Pawtucket will be demolished to make way for construction.
The Pawtucket tunnel is expected to take five years to complete. Tunnel boring is scheduled to begin in two years. The project is the first of four segments for Phase III. Additional connections and segments will be completed through 2041. This work will include sewer connections, a smaller tunnel link, additional wastewater storage, and green stormwater infrastructure.
CSO Phase I, completed in 2008, treats 1.1 billion gallons of wastewater from Greater Providence that would otherwise flow into Narragansett Bay. Phase II, completed in 2014, diverts 17 outflows from discharging into the Seekonk and Woonasquatucket rivers. The wastewater now runs into the Phase I collection tunnel.
The $548 million Pawtucket tunnel project received a loan covering half the cost from the Environmental Protection Agency. The Rhode Island Clean Water State Revolving Fund and other programs will also finance a portion of the project costs.